The specific aims of this project are to evaluate the placental transport and metabolism of serine, glycine, and leucine across the placenta of normal and IUGR pregnancies. Subsequently, alanine, glutamine and glutamate will also be studied. In so doing the studies will establish whether the striking differences in the transport of these amino acids found across the epitheliochorial placenta of the sheep is also found across the hemochorial placenta in man. Furthermore, since differences in amino acid concentration of IUGR versus normally grown fetuses have been reported, these studies will determine whether such differences are determined in an in vivo assessment of placental transport of these amino acids in IUGR pregnancies. In addition, by comparing data collected at mid gestation with those collected near term, changes in placental transport or metabolism of these amino acids will be studied. Carbohydrate studies will include determination of glucose disposal rate in pregnant and non-pregnant women, the former including both IUGR as well as multiple pregnancies to provide patients with a large variation in total conceptual mass. In this way the study will determine the relationships among maternal glucose concentration and conceptual mass versus maternal glucose production rate. In addition, by comparing fetal/maternal glucose MPEs, evidence of active fetal glucogenesis in IUGR pregnancies and pregnancies with low maternal glucose concentrations will be sought. Finally, an estimate of placental glucose transport will be obtained in IUGR versus normal pregnancies at cesarean section.